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Asteroids are an excellent source of natural resources (minerals, etc.) As stated in the U.S. fiscal year of 2014 budget, NASA requested $100 million to initiate plans to capture an asteroid, haul it into the lunar orbit, and send manned missions to the asteroid by 2025! Mining an asteroid in the future could help resupply rapidly depleting fossil fuels and natural minerals. Beside the apparent need for resources, NASA hopes to advance technological developments that will provide opportunities for “international cooperation, new industrial capabilities, and helping scientists better understand how to protect Earth if a large asteroid is every found on a collision course. You may have heard about the recent Russia Chelyabinsk meteorite incident. 1,500 injured and 7,000 buildings suffered. A small asteroid invaded Earth’s atmosphere and struck the ground in Russia. The shockwaves shattered thousands of windows!

NASA proposes identifying suitable targets, or asteroids 20 to 30 feet in diameter (extremely hard to spot) in favorable orbits (near Earth and small revolution) that would allow easy capture and transport to Earth. These desired small asteroids hit Earth on a regular basis; the asteroid that hit Russia was 50 feet in diameter. NASA’s Orion crew capsule and heavy-lift booster will send astronauts to the asteroid for sample returns. NASA has two teams working the proposed mission: one searching for suitable asteroids and developing unmanned technology to capture the asteroid, and another on future manned missions and sample collection.

In the wake of the asteroid (then meteorite) rocking Russia and a close call with an asteroid passing close to Earth on the same day, astronomers are extremely interested in asteroids.

What is the universe’s temperature? How has it changed and evolved? What causes the temperature to change? How is the temperature estimated? Is it continuously cooling or constant? –Pcelsus

Black Body Curve of the Cosmic Microwave Background

13.75 billion years ago, the Universe was much smaller and hotter. In the 1960s, Robert Dicke predicted a remnant “glow” from the Big Bang. In 1965 at the Bell Labs, radio astronomers Amo Penzias and Robert Wilson discovered that glow, named the cosmic microwave background radiation. The CBR was seen in all directions in empty space, with a black body curve (temperature ~3K in every direction). About 1 second after the Big Bang, the Universe was very hot, at ~1 billion K. At 3 minutes, protons and neutrons combine to form the nuclei of atoms. As space cooled, material condensed and atomic particles, then elements, molecules, stars, and galaxies formed. The hydrogen/ helium ratio (3:1) found today is about the same as what’s expected after the Big Bang. Atoms were “ionized” with electrons roaming free without being bound. At 300,000 years after the Big Bang, the Universe becomes transparent with a temperature of 3,000K. Light red-shifted by a factor of 1000, and the expansion of the Universe ensued.

Today, the Universe is 2.73K, or 2.73°C above absolute zero, but at the beginning of space and time, the Big Bang, the Universe reached over one billion degrees. From a single pinpoint, the Universe emerged as a scorching hot primordial soup of subatomic particles moving at high velocities. As the Universe expanded, the temperature cooled as more space was created and density decreased. The Universe is continuously cooling as it expands.

Measuring the temperature isn’t as simple as sticking a thermometer in space and waiting until it stabilizes at a certain temperature. Instead, scientists measure indirectly using the cosmic microwave background, or leftover radiation emitted by hot plasma 38,000 years after the Big Bang. As the Universe expanded, the electromagnetic waves of the CMR elongated and decreased in energy, leading to cooler temperatures. Using Planck’s law, scientists measured the black body radiation of the Universe. Planck’s law states that every object radiates electromagnetic energy according to temperature. Black body curves are lopsided, with the curve peaking at different wavelengths depending on the object. In fact, space has a nearly perfect black body curve, since physical objects tend to absorb and reflect light in certain wavelengths.

The UCI Observatory is located about a mile from the UCI campus. Though relatively small compared to famous observatories such as Keck Observatory in Hawaii or Kitt Peak Observatory in Arizona, the UCI Observatory serves basic viewing purposes. UCI Observatory dome houses a 24-inch telescope with a CCD camera and a 8-inch portable telescope. UCI professor Dr. Tammy Smecker-Hane and TAs Liuyi Pei, John Phillips, and Shea Garrison-Kimmel adjusted the telescopes and pointed them toward objects of interest, among which were the Ring Nebula, Mars, Saturn, star clusters, and a binary star system.

“As a bumpy, seat-wrangling dirt road emerges, a muddy, night-black SUV launches itself past ironclad gates. City lights twinkle to the left; hills lined with sharp grasses cast shadows to the right. Music blasts from speakers; Cosmonauts chatter nonstop, voices intermixed. A gray-white dome emerges and four shadows await, silently calibrating the 24 and 8-inch ocean-blue telescopes. As the sun dips beneath the horizon, night blankets the earth and icy air tackles my vest and slacks. First the moon, then Vega and Ursa Major— the true celestial sphere has appeared.” – Tianjia Liu

This past month (June 24, 2012- July 21, 2012), I attended the COSMOS (California State Summer School for Mathematics and Science) at the University of California, Irvine, with brilliant minds from Northern and Southern California, as well as other states. The 152 students were divided into 8 clusters. I was part of Cluster 2: Astronomy and Astrophysics. With 22 other COSMOS students, I ventured into the world of astronomy and astrophysics unraveled by UCI professors Dr. Tammy Smecker- Hane, Dr. James Bullock, Dr. Aaron Barth, Dr. Erik Tollerund, TAs John Phillips, Liuyi Pei, and Shea Garrison-Kimmel, and Teacher Fellow Lisa Taylor. I discovered that all students shared a strong passion for astronomy and high aptitudes for learning. It has been my honor to learn with the students, listen to the professors’ lectures, and follow the TAs’ instructions for CLEA (Contemporary Laboratory Experiences in Astronomy) Labs.

For a cumulative final, the TAs divided the class into 8 groups for Project Labs:

ABSTRACT: Stellar spectra are fundamental in understanding properties — temperature, spectral type, chemical composition, and mass — of stars. A spectrum is the amount of light that a star emits through narrow slit about 1 Angstrom in width. With the UCI Observatory’s 24-inch telescope and its photograph and ST-8 CCD camera, images of stars’ spectra — those of Arcturus, Vega (HD172167), and HD142780— were taken. Using the software program IRAF, the spectra were extracted, calibrated, and analyzed. Since stars are classified by spectral types, stellar spectra help distinguish a more massive and hotter star from a less massive and cooler star. Analyzing the strengths of absorption lines shows the stars’ compositions of elements such as hydrogen, helium, and calcium. While hotter stars such as Vega are more massive and have strong hydrogen absorption lines, cooler stars such as Arcturus are less massive and have strong neutral metals lines. Understanding stars’ properties leads to a better grasp of the past, present, and future of the Universe.

QUESTION: How can we use stellar spectra to determine the properties of stars such as spectral type, temperature, mass, and chemical composition?

Spectra of different elements including hydrogen, helium, and neon

BACKGROUND INFORMATION: Stars, actually infinitesimally small points of light, appear to twinkle because light refracts at Earth’s atmosphere. Held by gravity, stars shine due to nuclear fusion, its source of fuel. Their lifetimes depend primarily on mass; for their prime of life, stars, travel along the main sequence on the Hertzsprung- Russell, or Color- Magnitude Diagram. A stellar spectrum is the amount of light a star emits at a narrow wavelength interval (about 1 Angstrom, or 10^-10 meters). Each element has a distinguishable pattern of absorption lines (dark bands along the spectrum). Spectral types are a classification scheme developed by Annie Jump Cannon in the late 1800s and early 1900s. The spectral types are ordered in decreasing surface temperatures: O, B, A, F, G, K, M. Originally the classification scheme was A, B, C, D, etc. and stars were ordered according to the strengths of their Balmer (hydrogen) lines. Since stars with the strongest Balmer lines are not necessarily the hottest stars (hotter temperatures caused electrons to be excited and the atom to be ionized- lose electrons), the scheme was rearranged. The two stars analyzed were two variable stars: Arcturus of the constellation Boötes and Vega of the constellation Lyra.

CONCLUSION: By analyzing the absorption lines on the stars’ spectra, we determined the spectral types of each, thus allowing us to find their respective properties. The absence of hydrogen lines and prevalence of neutral metals in Arcturus’ spectrum allowed us to identify it as a K type star (Figure 1) . Vega’s spectrum contained strong hydrogen and ionized metal lines. Therefore we classified it as an A type star (Figure 2). Because the spectrum revealed absent hydrogen lines and visible neutral metals, we classified it as a M type star (Figure 3).

DISCUSSION: WHY DO STELLAR SPECTRA MATTER FOR THE FUTURE OF ASTRONOMY?

Map galaxies

Map the Universe

Learn about the lifetimes of different stars

Use information on old stars to learn about conditions after the Big Bang

Strong Nuclear Forces: protons in the nucleus repel by electrical forces, but strong nuclear forces, which can only occur at close distances, keep the atom together. As temperature rises, protons move faster. When 2 protons fuse, the output is 1 neutron, 1 positron, and 1 neutrino.

0.7% of the total mass of 4 protons is converted into energy, while 99.3% results in 1 helium nucleus. Some of the mass is converted into energy. Since E = mc², a little mass and release tremendous energy. While at rest, however, energy is equal to mass.

CNO Cycle

CNO (Carbon-Nitrogen-Oxygen) Cycle

The CNO Cycle is the main nuclear burning chain in main sequence stars hotter than the Sun. Using carbon as a catalyst to convert hydrogen into helium, the CNO cycle also converts 7% of hydrogen’s mass into energy; hydrogen fuses with carbon to form helium. 10% of the Sun’s nuclear fusion reactions is from the CNO Cycle. In 1967, Hans Bethe theorized on the energy production in stars.

Stars are held by gravity and shine because of the nuclear fusion reactions (fusing light nuclei into heavier nuclei, e.g. hydrogen atoms –> helium atoms) occurring in their cores. Luminosity and lifetime depend entirely on the star’s mass. Stars are composed of mainly hydrogen and helium, with trace amounts of other elements. Stars end their lives when they have exhausted their available nuclear fuel. Their final end states of stellar evolution are different and depend on mass.

OBSERVING STARS: Stars are so far away that they appear as infinitesimally tiny “points” of light.

What Do Astronomers Measure in Stars?

Brightness: Is the star constant or variable over time?

Spectrum: temperature and chemical composition

Color: temperature

Motion and Doppler Shift

Distance (measuring can be very difficult)

HOW MEASURING DISTANCE TO STARS IS IMPORTANT: Distance and magnitude can determine the star’s luminosity, or how much energy it’s generating and emitting. Distance to stars also determines the structures of galaxies. Then, measuring distances to galaxies can also determine the structure of the universe.

Parallax

MEASURING DISTANCE USING PARALLAX: Parallax is the apparent movement of a distant object when viewing from two different lines of sight. For example, hold out your thumb at arm’s length and close your right eye. Now, open your right eye and close your left eye. See the difference? Astronomers use distance the object “moved” and the angle from Earth and the object’s two different locations to determine the distance to that object. Earth’s motion acts as a baseline to measure the distance of a nearby star. As Earth moves around the Sun, a nearby star will appear to move slightly relative to distant background stars.

the star’s parallax = 1/2 the angular shift of the star over one year

parsec = parallax second of arc

1 parsec = the distance to a star whose parallax angle is one arcsecond

1 parsec = 3.26 light years

1 parsec = 3.08 x 1016 meters

distance (in parsecs) = 1/parallax angle (in arcseconds) –> d = 1/p

*Note: Parsec is NOT a unit of time, but a unit of distance! Arcminutes and arcseconds are NOT units of time, but units of rotation.

All stars have parallaxes smaller than 1 arcsecond. The nearest star, Proxima Centauri has a parallax of o.77 arcseconds and a distance of 1.3 parsecs. Parallaxes can be measures to 200 parsecs from ground-based telescopes. The GAIA Mission (2013), if launched successfully, will allow astronomers to measure 20 micro-arcseconds, or distances to 1 billion stars!

APPARENT MAGNITUDE: Apparent magnitude is how bright a star appears from Earth. On a logarithmic scale, a magnitude 1 star is 100 times brighter than a magnitude 6 star. Brighter stars have smaller magnitudes. The brightest star in the night sky is Sirius at -1.5. The faintest objects detected by the Hubble telescope are magnitude 30. Photometry is measuring the apparent brightness of an object.

Comparing Two Stars’ Apparent Magnitudes with an Equation

m2-m1 = -2.5 log10 (b2/b1)

m2 and m1 = apparent magnitudes of two stars

b2 and b1 = fluxes of two stars (flux is the amount of light energy received per unit of time per unit of area)

Apparent Magnitude Comparison

The Sun = -26.8

Full Moon = -12.6

Sirius = -1.5

Naked Eye (faintest objects) = +6

Hubble telescope (faintest objects) = +30

ABSOLUTE MAGNITUDE: Absolute magnitude is the actual luminosities of stars. The Sun has an absolute magnitude of 4.83.

Calculating Absolute Magnitude

m-M = -5 + 5 log10 (d/10 parsecs)

m = apparent magnitude

M = absolute magnitude

d = distance in parsecs

FILTERS & COLORS: Telescopes have filters that isolate specific wavelength regions of the wavelength. The most common filter is UBVRI. Different filters corresponds to different brightness. The ratio of brightness through two different filters correspond to the star’s color. The star’s color also determines the star’s temperature. The ratio between the star’s brightness through two different filters, such as the B and V filters, would be bB/bV.

(B-V) = (mB-mV) = -2.5 log10(bB-bV)

The B-V color index depends on the surface temperature of the star

The zeropoints are defined by the star Vega. Vega is 10,000 K and Vega’s color index for any filter combination is 0.

Stellar Spectra

STELLAR SPECTRUM: A star’s spectrum is close to a black-body (an ideal physical body that absorbs all electromagnetic waves) curve, with absorption lines imprinted on it by elements in the star’s photosphere. From the late 1800s to the early 1900s, Harvard College Observatory employed women to observe, map, and define all stars in the sky. When the observers disagreed on the classification of these stars, Annie Jump Cannon invented the spectral sequence base on the strength of stars’ Balmer absorption lines (Hα). Star with the strongest Hα lines were spectral type “A”, and the next strongest were type “B.” Later, however, some letters were removed. The astronomers discovered that the strength of Hα lines depends on the stars’ surface temperatures and stars with temperatures of 10,000 K have the strongest Hα lines. The sequence was then re-arranged in decreasing temperature, resulting in: O, B, A, F, G, K, and M. An acronym to remember the spectral types is “Oh Be aFine Girl/Guy, Kiss Me.” The subtypes range from 0 –> 9, with subtype 0 as the hottest and 9 the coolest.

Spectral Types and Corresponding Temperatures

O = >25,000 K

B = 11,000 K – 25,000 K

A = 7,500 K – 11,000 K

F = 6,000 K – 7,500 K

G = 5,000 K – 6,000 K

K = 3,800 K – 5,000 K

M = 2,200 K – 3,800 K

L, T = <2,200 K

* Spectral Types L and T are the recently discovered brown dwarfs, or stars too small for nuclear fusion

In addition to the spectral type and the subtype, each star also has a class. For example, the Sun is G2V (V means main sequence star). While a M0 main sequence star may have 0.6 R☉ and 0.06 L☉, a M0 red giant star will have 40 R☉ and 300 R☉.

RADIUS: The Sun’s radius is 696,000 km, or 1 R☉. A Red Giant is 50 – 100 R☉. A White Dwarf is about 0.01 R☉.

MASS: The Sun’s mass is 1.989 x 10³º kg, or 1 M☉. 1 M☉ is 330,000 times Earth’s mass. Masses of stars range from 0.08 M☉ to over 100 M☉.

H-R Diagram: Majority of Stars in the Main Sequence; Very Few Stars as Red Giants or White Dwarfs

H-R DIAGRAM: The Hertzsprung-Russell (Color-Magnitude) Diagram organizes the stars into a plot graph, based on color (spectral type)/ temperature and luminosity/ absolute magnitude.

Main Sequence: normal stars in their prime of life fusing hydrogen into helium

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Astronomy: To Infinity and Beyond! Welcome to "The Cosmos." I will take you on a journey through our solar system, galaxy, and the Universe! You will be updated with current events in astronomy. Please click on the picture above to visit my blog on poetry, writings, and musings!

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References for photos used from websites can be found under the "References" page. Photo credit: news sites (reference included in post), NASA (most images used), and Google (for artists' view of objects unable to be photographed).